Most Protestant/evangelical sects don’t preach an “underground” church but rather a “universal” or “invisible” one comprising all people who believe directly on Christ for eternal salvation. Baptists have a long history of bitter difference with the CoC over just this kind of issue, the CoC being almost as dogmatic as the RCC about the unique power of baptism in their local houses of worship, and the Baptists saying no, salvation is based on personal relationship with Christ which in turn is based on hearing the Bible message, and baptism is a ceremony of witness. The Baptists match up with most other Protestants and evangelicals in this regard. The question of canonical Christian scripture was settled before the church got into anything which is anathema to most Protestants and evangelicals (e.g. alliance with a pagan government).